1. Field of the Invention
This invention relates to flexible disc devices for storing information, and more particularly to systems for securing compatibility between memory media of different track density and to a magnet head assembly suitable for use in the system.
2. Description of the Prior Art
In recent years, there has been remarkable development in magnetic recording technology, and recording density of information devices such as a magnetic disc device or a flexible disc device has been improved significantly.
In order to realize the high recording density, the line recording density per track and also the track density have been raised. In a flexible disc device of the exchangeable medium type used as a file, the track density has also been rapidly improved. Although 48 tracks per inch (hereinafter referred to as TPI) were usually used in small devices in the prior art, there has been increasing use of 96 TPI recently and this use is increasing further.
This increasing use of 96 TPI has created a problem. Change in the track density results in change of the device as a whole, and since it is difficult for a medium recorded in a new device of 96 TPI to be reproduced or recorded in conventional device of 48 TPI, the medium must be used only in the original device in the present practice. Accordingly, if media recorded in devices of 48 TPI and 96 TPI can be mutually recorded and reproduced, there will be substantial economic benefit.
Prior art relating to a flexible disc device of high density will now be described.
In order to realize a flexible disc of high density, one conventional device distinguishes difference in the coercive force of the recording medium or the magnetic property of the coated film thickness. In such a device, a notch is provided at a specific position of a jacket so as to prevent the data error which would occur by the use of high-density medium in a conventional device or inversely the use of ordinary medium in a high-density device and to detect the mistake in use. The device is so constituted that a medium discrimination detector A informs an operator of mistake a in setting a flexible disc, and the information is transmitted through a medium setting error detecting circuit B and a signal connector to a host computer C as shown in FIG. 1. In a series of operations, information concerning the mistake is provided to the operator and the host computer C so as to inhibit incorrect writing or reading action.
In addition, FIG. 1 shows many circuits and elements without reference numerals. Since the basic function of these elements is known by those skilled in the art and the elements do not relate directly to this invention, description of these elements is omitted at this point and will be supplied when required in the course of this disclosure.
Another device of 96 TPI can be used for both a high density medium and an ordinary medium. In such a device, use of an inside track having a high line recording density is inhibited when using an ordinary medium and the writing current is changed corresponding to the difference in the properties of the medium.
However, such discrimination signal is not used for changing the track density in the prior art. FIG. 1 shows a conventional example particularly utilizing the high density medium, except that devices commonly used in the prior art had no medium discrimination detector.
Regarding the compatibility between devices or media which are different in track width, information of 48 TPI written in the same medium property, i.e. the same line recording density, can be read by a device of 96 TPI in prior art. This is because the center portion of a track in 48 TPI is made coincident with that of a track of even number in 96 TPI.
On the contrary, information written in a device of 96 TPI cannot be read by a device of 48 TPI in the prior art. If information is written only in tracks of even number in 96 TPI, the effective width of the information track becomes 1/2 but appreciable trouble does not occur. However, various noise such as old information in the track position of the odd number tracks is read by the wide head of 48 TPI in this state, and the disturbing noise decreases the signal-to-noise ratio.
Accordingly, in the prior art, a disc recorded in a device of 48 TPI can be read by a device of 96 TPI; a disc recorded in 96 TPI cannot be read by a device of 48 TPI. That is, the compatibility of mutual medium writing does not exist in the full sense.